On Tue, Aug 22, 2017 at 04:13:54PM -0400, Daniel Richard G. wrote:
> Hello list,
>
> I'm writing in to report a bizarre issue with the IBM z/OS XLC compiler
> that is currently causing one gnulib test to fail (test-timespec), and
> may present an issue for application code simply because no other
> compiler does things this way. My hope is to have gnulib integrate a
> workaround so that this won't bite anyone else.
>
> I have been in contact with IBM about this, originally reporting the
> issue as a compiler bug. However, they responded that the compiler
> behavior is conformant to the C standard and that they are less
> concerned with matching the behavior of other systems than keeping
> things as-is for the benefit of existing customer application code.
>
> The problem has to do with the implicit integer type that is used for
> enum symbols. Here is a sample program that illustrates the issue:
>
> --------8<--------
> #include <stdio.h>
>
> enum { BILLION = 1000000000 };
>
> static const unsigned int BILLION2 = 1000000000;
>
> int main(void) {
> int x = -999999999;
> printf("BILLION = %d\n", (int)BILLION);
> printf("x = %d\n", x);
> printf("x / BILLION = %d\n", (int)(x / BILLION));
> return 0;
> }
> -------->8--------
>
> On GNU/Linux and AIX, with a minimal compiler invocation, this
> program prints
>
> BILLION = 1000000000
> x = -999999999
> x / BILLION = 0
>
> However, on z/OS, it prints
>
> BILLION = 1000000000
> x = -999999999
> x / BILLION = 3
>
> What happens is that BILLION is implicitly typed as an unsigned int,
> rather than an int. If you edit the code above to use BILLION2 instead
> of BILLION, you'll see the same result on GNU/Linux.
It's odd that they claim that this conforms to the C standard. C11
says, in section 6.4.4.3 "Enumeration constants":
An identifier declared as an enumeration constant has type int.
It also says in section 6.7.2.2 "Enumeration specifiers":
The identifiers in an enumerator list are declared as constants that
have type int and may appear wherever such are permitted.
This seems pretty clear to me, so I wonder how this interpretation
arises.
